Two-cycle scavenging internalcombustion engine



May 12, 1953 E. w. SPANNHAKE 2,638,081

Two-CYCLE scAvENGING INTERNAL-coMBusTroN ENGINE Filed Jan. 24, 1950 4`SheetS-Sheet l @Wn/Q U May l2, 1953 E. w. SPANNHAKE 2,638,081

` Two-cYcLE scAvENGING INTERNAL-COMBUSTION ENGINE Filed Jan. 24, 1950 4 Sheets-Sheet 2 ATTORNEYS.

May 12| 1953 E. w. sPANNHAKE 2,638,081

TWO-CYCLE SCAVENGING INTERNAL-COMBUSTION ENGINE Filed Jan. 24, 1950 4 Sheets-$heet C5 INVENTOR.'

ATTORNY i INVENTOR.' 2 @5% a?" E. w, SPANNHAKE 2,638,081 Two-CYCLE SCAVENGING INTERNAL-COMBUSTION ENGINE 4 Sheets-Sheet 4 BY/mn, @6%

May 12, 1953 Flled Jan 24, 1950 Patented May 12, 1953 TWO-CYCLE SCAVENGING INTERNAL- COMBUSTION ENGINE Ernst W. Spannhake, Park Forest, Ill., assignor to Barnes & Reinecke, Inc., Chicago, Ill., a corporation of Delaware Application January 24, 1950, Serial No. 140,285

13 Claims. l

This invention relates to an improved internal combustion engine and cylinder therefor wherein scavenging and charging is accomplished by a new method of air flow permitting high speed port controlled twoy cycle engine operation with relatively low scavenging pressure and correspondingly high efficiency.

The apparatus of the present invention is characterized by utilization of the circular symmetry inherent in all practical engines to define effective iiow paths for admission of air and exhaustion of products of combustion. These symmetrical now paths efficiently carry the entering air and the products of combustion in separate streams of large cross-sectional area and relatively uniform velocity so that the undesired products of combustion are effectively replaced by the combustion-supporting air during the momentary portion of each cycle when the-ports are uncovered and a minimum degree of eddy flow is created.

The structure of the present invention also utilizes exhaust port orientations that facilitate the exhaust air flow from the downwardly descending symmetrical air column created by the central symmetrical intake air now. This exhaust port orientation greatly reduces and practically eliminates short circuit air flow direct from the intake ports toy the exhaust ports and (Cl. 12B-65) Still another object of the present invention is to provide an improved internal combustion engine piston adapted to direct the intake gases upwardly and at the same time minimize eddy flow of the same.

Another object of the present invention is to provide an improved internal combustion engine and cylinder construction therefor wherein the intake air how exerts maximum cooling effect on the piston.

The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claims. My invention itself, however, both as to its organization and mode of operation, together with further objects and advantages thereof, may best be understood .by reference to the following description taken in conjunction with the accompanying drawings, in which:

Figure 1 is an axial cross-sectional view through the cylinder of a complete diesel engine constructed in accordance with the principles of the present invention;

Figure 2 is a fragmentary enlarged portion of Figure 1 showing in detail the air intake and exhaust ports;

Figure 2a is a fragmentary reduced crosssectional view through axis 2a-2a, Figure 2;

Figures 3, 4, and 5 are views like Figure 2 showthe attendant ineinciencies. In fact, with the so ine additional embodiments 0f the present inconformations described herein, the throttling VentOIl;

effect which would result from such short cir- Figure 6 iS an -aXial @OSS-Sectional View cuit now is so great that the resultant frictional through the Cylinder 0f a 60111D1617@ diesel engine iiow resistance would exceed that of the entire constructed in accordance with the principles of normal flow path through the cylinder and there- 3.5 an alternative embodiment of the present invenby prevent it from coming into existence. tion;

It is therefore a general object of the present Figure 7 is a fragmentary View 0f the structure invention to provide an improved internal comof Figure 6 showing the piston in the lowermost bustion engine and cylinder therefor wherein iposition Where it uncovers both exhaust and infull advantage is taken of the symmetry of the 4o take ports; cylinder construction to improve scavenging. Figure 8 is a top plan view of the crown por- Another object of the present invention is to tion of a piston constructed in accordance with provide an internal combustion engine and cylstill another embodiment of the present inven- :inder therefor wherein the portion of operating tion; and, cycle required for scavenging is minimized and 45 Figure 9 is a cross-section view through axis the fiow resistance to scavenging air through the 9-9, Figure 8. ports is maintained at a relatively low value. Referring now to Figure l, there is shown at I0 Further it is an object of the present invention a cylinder block dened by a series of mating to provide an improved internal combustion parts Illa to If sandwiched together and held in engine particularly suitable for high speed port s() snug engagement by the bolts I2 having nuts I2a.

controlled diesel engine operation.

Yet another object of the present invention is to provide an improved `internal i combustion engine with eihcent scavenging wherein the axial length of the space occupied by the intake and exhaust ports is minimized.

The bolts I2 receive sleeves I4 between members Ib, IGC, and Ind to denne intake and exhaust manifolds I5 and I8, respectively. A liner or sleeve 20 is received in the cylinder block I0 and iits snugly against the annular seat 22 formed in head IDf to deiine a closed cylinder.

The head portion if of the block lil has a centrally symmetrical bore 2d. In the specific embodiment shown. this bore is of conical shape and is stepped into the surrounding aluminum material. This bore is lined. with a heat resisting materia-l as stainless steel, having a value of thermal conductivity that does not pri duce excessive cooling which together with the complementary part of thepiston crown, defines a soace of predetermined size and'hieh wall temperatur@ into which the fuel is injected. While the seace so defined is of conical shape in. the specic structure shown in Figure 1. other cene trally symmetrical coniigurations, such as a sphere or half-sphere may be used and in some cases will operate more effectively. v

A finned cylindrical member 23 surrounds the liner 28 in the region immediately below head i iiff This member' reinforces the liner 2! and deiines air passages 25a through which cylinder cooling air llow takes place,

A piston is slidably receivedin the cylinder liner 2d. The piston carries a'wrist pin 32 Awhich receives the connecting rod 3ft. The wrist pin 32 defines the inner member of a sleeve bearing Whereas the connecting' rod forms the outer member thereof to permit rocking motions of' the connecting'rod as the piston reciprocates. The opposite end of the connecting rod has a semicylindrical sleeve bearing surface' which is completed by the detachable complementary hearing d-eiining member 3dfx which isY attached to the connecting rod 34 by thebolts 353.

The sleeve hearing formed on the end of the connecting rod 35 receives the eccentricV portion 33a of the crank shaft 3S. Consequently, asthe crank shaft t3 is rotated the piston li'l executes reciprocating motion. The counterbalance fill balances the crank shaft 33 to reduce the'vibratory forces incidentto the unbalanced eccentric portion lilla/'of the crankshaft and theYconnectingv rod 34. i

It will. be noted that the crankshaft dii and the connecting rod covniinethe piston 3!! in the customary Way to .reciprocating movements `hav ing a predetermined throw. The maximumpisi Iton ymovement,in the upward direction oi Figure .l brings the face of` the piston almostin contact withfthe cylinder head Ulf .and the maximum movement of the piston in the downward direce tion just-clears the intake ports i2 asis described in further detailhereafter. In eeneralyit is desirable to have the vpiston clear the ports withv a minimum overshoot, since this reduces thedead portion of the operating cycle when no work is being done. Moreover, will .be described' in further detail hereafter, overshoot decreases the guiding effect of the piston face and thus detracts from the efficiency of scavenging.

The top face of the piston 3i! is donned hy the removable disk 4d which has a. threaded stud portion 44a extending through the upper part of the piston. This stud receives the bolt fili which securely holds the dish t4 in position onv the piston. In the speciiic embodiment shown in Figure l, the upper face of disk Mt is symmetrically cupped to denne a low friction surface against which the'air is directed. This struct-ure is described in further detail hereafter.

The underside "of the disk M is provided with an annular groove Mb which communicates with the edge of the cylinder through the annular passages.. gibieasV shown. This structure isv described and. claimedin my copending patent application S. N. 160,886, ledr May 9, 1950', en-

titled Internal Combustion Engine and Piston for Use Therewith. Briefly, it affords a heat harF rier permitting the upper piston ring it and. adjacent portions of the piston to operate well below the coking point of the fuel, It also denes a pressure'relief space toreduce the pressure across thel'ower piston ring-s dil in the event the upper ring 43 fails.

The fuel injector is indicated generally at Briefly; uelunder pressure is supplied through injection tubing Eli to the fuel injector 52 which denes a passage closed hy a valve and opening into the top of the symmetrical dome defined, oy lining 2li. The fuel injector is actuated in sequence with themovements of piston et to force a'A metered quantity of fuel into the cylinder at essentially the time the piston reaches the mum compression point shown in Figure l.

Immediately above the cylinder head lili, the fueliniectorV t2-has iins 52a.; These ns are annular in, shape and t in asuitablc bore inthe longitudinal'cylinderhead ii'nsii; As the coolingair ilows along the main iinsiii it lows into the spaceoetween'each pair of adjacent fins 52a, and around the injector'tovcool ther same. This prevents clogging of the injector oy the fuel. This structure described and claimed in my copendingv patent application S. N. l82i2'll, filed August 30,1950, entitled internal Combustion Engine' andFuel Injcctorior Use-Therewith.

in' accordance with the present invention, the. airis taken into the cylinder 2i) andthe exhaust gases withdrawn through two sets' oi syminetifically disposed ports axially spacedrelatiye to the cylinder. The intake ports lll', Figures l and 2, communicate with the intake manifold it as shown-'fand are directed in a primarily radial direction with vaislight downward tilt relation to the piston tcp face. 'The exhaust ports communicate vwiththeexhaust manifoldV iiiy and also have axialftilt as w-illh'e evident from Figures 1 and 2.

The orientationoi the-intake kand exhaust ports aboutk the periphery ofv the cylinder 2Q is best seen in FigurerZa which isa cross-sectional view through axis Fla-Zai Figure 2. As shown, the ports are uniformly spaced` about theliner 29 and the ports ofeach set are symmetrical relative to--the cylinder. Moreover, as seen in the crosssection, theA portsV alternate so that each port 2 is between a pair of adjacent portsl 5E andy vice versa.

As will be. evident from Figures l., 2, and 2c. the por-ts 42. are-directedr radially of the cylinder and have a slight. downward tilt in relation to the piston top face This causes the intake air to rushv to thecenter ofthe cylinder when the ports arefuncoveredl and-thereafter to rise in a central columni,l Figure 2. Thisstream flows upwardly inthe Icenter of the cylinder until it strikes the head` Hij Where it is deflected downwardly and outwardly asshown hy the arrows E52. The air stream then descends adjacent the walls of the cylinder inl an annular downward dow lill which is readilyy drawn into the exhaust passages 58 which have a substantial axial tilt in the upward direction and receive'the downward flowing air Without substantial change in direction Of flow.

In the engine of Figures l, 2, and 2a, it will be evident that the air flow takes place symmetrically relative` to the axis of. the cylinder. Blier-cover,` the lowlines do not'` yconcentrate at any points other than the ports so that there is a minimum tendency for eddys andv turbulence acaaosi and a maximum tendency for separation between intake and exhaust air and minimum scaveng ing power requirements.

Moreover, the cool intake air stream is directed across the face of piston 30 so that it receives guidance therefrom.

One requirement essential to the creation of a central column of upwardly flowing intake air isv that the air impinge upon and be guided by the face of the piston. Unless the intake air is so directed, it is likely to deviate from the central upward now and flow directly into the ex haust ports or hug one portion of the cylinder wall. Either of these conditions -results in passage of the intake air through the cylinder without effectively displacing the undesirable products of combustion from the prior stroke. While central flow can be enforced by exceedingly powerful intake jets created by ports Whose area is small in comparison with the cylinder dimensions, this expedient demands high scavenging pressure with the incident power losses and reduced engine eiciency.

I have further found that the air flow can be practically directed across the face of the piston only by directing the air flow coming out of the intake ports to impinge upon the face of the piston from its outermost portions on and at at least a small angle relative thereto. An additional effect of this flow configuration is the cooling elect on the piston which permits operation at higher power outputs than would otherwise be possible within fixed limits of piston tem'- perature.

The structure of Figures l, 2, and 2a is subject to the disadvantage that the port space is limited by the portion of the cylinder at crosssection 2d where the ports 42 and 58 cross. This limits the maximum cross-sectional area of the ports and consequently increases the pressure differential required for scavenging. l In the alternative structure of Figure 3, this problem is overcome by spacing the ports 58a and 42a a sufancient distance axially of the cylinder to avoid the crossed ports. Each set of ports can then be made of the maximum size permitted by the cylinder dimensions without regard to the other set.

As shown in Figure 3, the ports 58a and 42a. are somewhat greater in number and larger in size than the ports 58 and 42, Figure 2. The available total port cross-sectional area is accordingly increased and the pressure and power required for scavenging i'low accordingly reduced.

Figure 3 also shows a modified construction of the cap portion "lll of the piston 30. In the modiiied form shown in this view, the cap 44a has an upstanding air guiding protuberance Mb which defiects the air upwardly as it impinges thereon from' the intake ports 42a. This protubere-nce supplements the action of the air streams issuingr from the opposed ports in directing the air upwardly. The protuberance has the further advantage of dening a gradually curved space for air flow and overcoming any tendency for eddy now at the center of the upper surface of the cap M.

Figures 8 and 9 are top plan and cross-sectional views, respectively, of a piston cap or crown embodying a modified form of the piston structure of Figure 3. The piston crown in this case embodies a central protuberance i441) which guides the air in the same fashion as the protuberance Mib, Figure 3. However, a plurality of radial iins |440 extend about the protuberance as shown and extend outwardly from the protu- 6. berance by a distance substantially equal to its thickness.

The piston crown of Figures 8 and 9 may be attached to the piston of Figure 1 to define a complete engine. When the piston reaches the end of its downstroke, the intake ports 42, Figure 1, are uncovered to cause a series of jets spaced about the periphery of the piston to impinge upon the surface of the crown as shown by the arrows |45, Figure 9. These jets travel into the spaces between the adjacent fins and are deflected upwardly as shown by the arrows |46, Figure 9, to form a central column of upwardly flowing air. The fins guide the air stream in a purely noncircumferential direction with minimum tendency for eddy now.

In Figure 4, the intake ports 2b are of rectangular cross-section and the exhaust ports 58h are of like cross-section. The advantage of this cross-section resides in the improved utilization of the available cylinder area in the region the oppositely directed ports overlap. l In the structure of Figure 5, the intake ports 42o and the exhaust ports 58o are oriented in the same direction, both being pointed towards the head of the cylinder. The ports do not cross, thus making the whole cylinder area available for each set of ports. The intake air is deilected downwardly against the piston face by a series of varies mounted in each port 42o. These deflect the air just as it leaves each port to change the upward velocity component to a downward velocity component. This is shown by the arrows 68 which show the direction of air flow at various points in the ports.

It will be observed that in the structure of Figure 5 the number and size of the ports 42o and 5de is increased over the structures of Figures 2 and 4 and at the saine time the spacing between the adjacent sets of ports is made smaller than in the structure of Figure 3. Consequently, ports of maximum size are achieved without a corresponding increase in the portion of the pis' ton stroke during which the ports are uncovered` Figures 6 and show an engine constructed in accordance with a further embodiment of the present invention where the desired central air column is achieved with intake and exhaust ports oriented substantially parallel and yet the intake air impinges on the piston face without any air deflecting vanes. In Figures 6 and 7 parts corresponding to parts shown in Figure l are given like numbers except that Zilli has been added to each.

The engine of .Figure 6 is constructed generally like the engine of Figure l except that the additional sleeve 2mg is sandwiched between the parts Zlile and Milf. A cap lill with ns Ella is itted in the space thus defined between the part 2me which carries ns 228e, and the cylinder head Zilli. The 2li delines the conical outer portion of the cavity provided at the top of the cylinder to mate with and receive the crown portion 264 of the piston 23d. ln a production engine the cap 2i l is preferably formed unitarily with the cylinder head Zlilf.

A precombustion chamber of somewhat spherical shape is defined the cylinder of Figure 6 by the lining 22E formed in the cylinder head tiilf. Fuel is injected into this chamber atapproximately the point in the stroke shown in Figure 6.

The crown 2h14 of the piston 230 of Figure 5 if of conical shape with a attened top portion 2Mo., Figure 6. The slope of this crown is slightly greater than the slope of` the intake ports 242 as seeni best in Figure 7. Consequently, as the intake air travels through the ports it iinpinges'on'thejcrown ataslightangle as indi cated by ythe'arrowsii", and is directed upwardly inra central .air column as indicated by arrows 26h The air thereupon impinges on the cylinder head tobe 'deflectedoutwardly and back shown bythonarrows- ,then travels through the outlet. ports 25d' into. the exhaust manifold as shown `by thefarrows 2 65;

, .While air from the intake jets of the struc ture of Figures 6 and T iinpingesat a smallagainst: the piston face, the intake ports are'neverthelessoriented substantially parallel to th'efexhaust ports lli-tf. Consequently the avail-- able cylinder area is effectively used for porting and the'mexiniuml port area availal'ile with the cylinder .dimensions involved is achieved. Yet the saine tircewtlie` axial dista.. e between` the openingsof the-respective groups or ports is n inimiaedand-the dead portion ofthe piston stroke thereby made small.

Whilesuuare-orrcctangulariports may be used with thefstructureorFiauresfl and '2, round ports are most simple to form and, with the effective usc'of the cylinder siaeassociated with the stru ture shown, have been found' quite adequate some' engines;

It will be observed that in allv the forms of the present vinvention the exhaust and intake ports are arranged in two'symmetrical arrays the bottom limit or the piston stroke. The ports opening into-the cylinderat points adjacent the lilnitbf piston throw areintake ports and direct the airA in a direction ixed by the fact that it has nol circumferential component and impinges on. thev piston top face at a slight angle either because of portorientation or because of air defleeting elementsas shown in Figure 5. The

other ports'are exhaust ports adapted to receive exhaustgases `flow-ing ina primarilyv axially down ward direction by reason of their upward tilt. Ihave usedthe term upward herein to designatethe direction. a Jay from the limit of pieton throw nea-r which the ports are located. By upward, tilt of aport. I. mean that the opening oi the port into the cylinder is positioned upwardly relative tothe adjacent portions of the port.

While I have shown and described the present invention as applied to an air cooled diesel engine', it will be apparent that it applicable to other internal combustion engines, such as gasolineengin'espwhether air cooled or w-,ter cooled.

In ,theaccompanying claims l have referred to the ports tile, Figure 5, as the trailing ports. These are behind ports 58e in the direction the ports are directed.

It willbe observed that the exhaust ports are located, above the intake ports sothat the piston uncovers the exhaust ports before uncovering the intake ports. This provides a' suicient blow down to reduce the cylinder'pressure below the pressure in the'intake manifold before the intake ports'arev uncovered, thus avoiding countertlow without the necessity of valves.

While I have shown and described particular embodimentsof my invention, it will .of course be understood that l do not wish to be limited theretoand that by the appended claims I intend 'to cover all modifications and alternative constructions` falling within the true spirit and scope of inyinvention.

What I'. claim as new and desire to secure by Letters Patentof the United States is:

l. In a two-cycle internal combustion engine about the cylinder adjacent one limit of piston throw 'and adapted to` direct air inV a non-,circuinerential downward direction against `.the piston face,and a plurality of. exhaust ports.` ar'- ranged symmetrically about thecylinder adjacent the intake ports onthe side opposite said. limit of lpiston throw; the eXhaust-portsbeing adapted toreceive air ilowing in av primarily axially downward direction.

2. In a two-cyclev internal combustion engine the improvement-comprising a-cylinder, a piston in the cylinder havinga symmetrically dished face with a symmetrical centrally disposed flowdirecting protuberance, meansy operative to conne the piston to reciprocating movements of predetermined throw, a. plurality or intake ports arranged symmetrically about the cylinder adjacent one limit of piston-throw and adaptedto direct` air in a non-circuniferential direction againstthe face of the piston,.and'a plurality` of exhaust ports arranged symmetricallyk about the cylinder adjacent they intake ports'on the side opposite said limit of` piston throw, the exhaust ports beingadapted tofreceive air flowing` inl a primarily axially downwardk direction.

3, ln a twwcycleinternal combustionengine the improvement comprising a cylinder, a piston in the cylinder having a symmetrically dished face with a symmetrical centrally disposed flowdirecting protuberance and radial vanes symmetrically disposed about the protuberance, means operativey to conne the piston to recip rocating movements of predetermined throw, a plurality or intake ports arranged symmetrically about the cylinder `adjacent one limit ofv piston throw and adapted to directv airin a. non-circumferential direction against the face of the piston, and aplurality of exhaust portsarranged symmetrically about the cylinder' adjacentv the intake ports on the side oppositesaid limitl of piston throw, the exhaust ports being adapted'to receive air flowing in a primarily axially down- 'ard direction.

e. In a two-cycle internal'combustion engine the improvement comprising a cylinder, a piston in. the cylinder, means operative to corinne the piston to reciprocating movements of predetermined throw, saidcylinder having a plurality o symmetrical staggered intake `and exhaustports adjacent one limit' of piston' throw, the intake ports being directed towards said limit of piston throw and the exhaust ports being directed away from said limit of piston throw, the intake ports being disposed in a ring nearer said limit ofpis'- ton throw than the exhaust ports and being oriented to direct 'the intake air againstthe lace or the piston.

5. ln a two-cycle internal combustion engine the improvement comprising a cylinder, a piston in the cylinder, means operative to confine the piston to reciprocating movements of predetermnedV throw, said cylinder having. aplurality of. symmetrical .intake and exhaust portsadjacent one limit of piston throw, the intake-ports being directed towards said limit of piston throw and the. exhaust ports being directed away from said limit oi piston throw, the intake ports being disposed in airing nearer said limit of piston throw than the exhaust ports and being oriented to direct the intake air against the face of the piston.

6. In a two-cycle internal combustion engine the improvement comprising a cylinder, a piston in the cylinder, means operative to conne the piston to reciprocating movements of predetermined throw, said cylinder having a plurality of intake ports arranged symmetrically about the cylinder adjacent one limit of piston throw and oriented non-circumferential directions away from said limit of piston throw, air deflecting vanes in said ports oriented to direct intake air against theface of the piston, and a plurality of exhaust ports arranged symmetrically about the cylinder adjacent the intake ports on the side opposite said limit of piston throw and oriented substantially parallel to the intake ports.

7. In a two-cycle internal combustion engine the improvement comprising a cylinder, a piston in the cylinder, having a conical face of predetermined slope, means operative to conne the piston to reciprocating movements of predetermined throw, said cylinder having a plurality of intake ports arranged symmetrically about the cylinder adjacent one limit of piston throw and oriented in non-circumferential directions away from said limit of piston throw at smaller slope than the slope of said face, and a plurality of l exhaust ports arranged symmetrically about the cylinder adjacent the intake ports on the side opposite said limit of piston throw and oriented substantially parallel to the intake ports.

8. A cylinder structure for an internal combustion engine comprising a member with a cylindrical bore having an axis and two series of ports arranged symmetrically about the bore at adja-A cent axial position, one series of ports being oriented in a non-circumferential direction and the other series being oriented in a primarily axial direction pointed away from the rst series of ports.

9. A cylinder structure for an internal combustion engine comprising a member with a cylindrical bore having an axis and two series of ports arranged'symmetrically about the bore at adjacent axial positions, one series of ports being oriented in a non-circumferential direction with axial tilt away from the other series of ports and the other series of ports being oriented in a primarily axial direction away from the iirst series of ports.

10. A cylinder structure for an internal combustion engine comprising a member with a cylindrical bore having an axis and a series of ports alternately directed relative to the axis of the cylinder symmetrically disposed about the bore, the ports oriented in one direction opening at one axial point in the bore and the ports oriented in tion with small axial velocity component.

12. A cylinder structure for an internal combustion engine comprising a memberwith a cylindrical bore having an axis and two series of ports symmetrically disposed about y.the cylinder x at adjacent axial positions, the ports being oriented in substantially parallel relation with substantial tilt in the axial direction.

y 13, In a, port-controlled internalv combustion engine characterized by efhcient scavenging, the

vcombination comprising a cylinder with a head at one end, a piston within the cylinder having a non-planar inner face,means to confine the piston to predetermined reciprocating motions toward and away from the head, the cylinder having a, symmetrical set of intake ports located adjacent the outer limit of piston throw and operable in cooperation with the piston to create a central upward air column, and a symmetrical set of exhaust ports positioned inwardly of said intake ports and having primarily axially upward orientations to receive the descending annular column of air, said inlet ports being oriented to .direct the incoming air against the inner face of said piston at an angle thereto, and said inner piston face having a non-planar, symmetrical configuration deflecting the streams of incoming air upwardly in a centrally symmetrical pattern within said cylinder.

ERNST W. SPANNHAKE.

References cited in the me of this patent UNITED STATES PATENTS Number Name Date 856,647 Maud June 11, 1907 1,374,573 Imhoff Apr. 12, 1921 1,587,585 Hansen June 8, 1926 1,622,717 Hildebrand Mar. 29, 1927 1,727,697 Bullnheimer Sept. l0, 1929 1,781,194 Riehm No'v. l1, 1930 2,002,668 Lack May 28, 1935 2,016,344 Simmen Oct. 8, 1935 2,047,785 Kreuzer vJuly 14, 1936 2,209,996 Neuland Aug. 6, 1940 FOREIGN PATENTS Number Country Date 534,265 France of 1922 

